Landscape vs local effects on insect herbivory in fragmented calcareous grasslands

MARIA ROSA ROSSETTI; RÖSCH VERENA; MARTÍN VIDELA; TEJA TSCHARNTKE Y PÉTER BATÁRY

Göttingen

Congreso; 45th Annual Meeting of the Ecological Society of Germany, Austria and Switzerland; 2015

Insect herbivory can shape the structure of plant communities by influencing the competitive dynamics among plant individuals. Herbivory patterns depend on factors acting at different spatial scales. Habitat fragmentation, the reduction of habitat fragment size and increasing habitat isolation, is a landscape level effect and can cause species loss of herbivores that in turn may decrease herbivory. Composition and configuration of the surrounding landscape can influence species movement among habitat fragments, potentially leading to alterations of herbivory. Additionally, other factors operating at the local scale like vegetation height and species richness of plants can directly affect herbivore diversity and herbivory. This study aimed to examine the relative effects of landscape fragmentation (fragment size, connectivity of fragments and percentage of arable land in the surrounding landscape) and local characteristics within fragments (herb species richness and height, grass cover and bare soil) on insect herbivory. We selected 28 calcareous grasslands in Central Germany, one of the ecosystems with the highest diversity of plant and animal species in Europe. We measured leaf area damaged through visual inspection of all herbs in 12 plots (50 × 50 cm) per fragment. Grass cover, species richness and height of herbs and bare soil were estimated in each plot. Herbivory was analysed with general linear models. Herbivory was positively related to grass cover and herb height at the local scale and higher in small than large grasslands as the only landscape influence. The effects of the local predictors were stronger than the landscape effect. Higher herbivore pressure at increasing grass cover and herb height could be associated with herbivore concentration on the remaining and more apparent herbs. The landscape effect could imply that herbivores may be released from natural enemy control and increase their damage in small grasslands.